Acid cadmium electroplating bath



Patented Nov. 19, 1940 so STATES ACID CADMIUM ELECTROPLATING BATH Henry Brown, Detroit, Mich, assignor, by mesne assignments, to The Udylite Corporation, a corporation of Delaware No Drawing. Application February 18, 1937, Serial No. 126,429

14 Claims.

This invention relates to an acid cadmium electroplating bath, and more particularly to an acid bath that gives a ductile matte plate with a er bond to steel than with cyanide cadmiumbaths. Also in plating on aluminum alloys this acid cadmium bath gives better adherence although the difference is not as great as with steel. The conductivity of the acid cadmium bath is greater than that of the cyanide bath which makes it more advantageous in barrel plating. In still plating the acid cadmium bath permits the use of higher cathode current densities as Well as higher anode current densities. The latter fact makes possible the use of smaller anode areas without polarization effects.

There has been comparatively little work pub lished on acid cadmium baths. This is due, in no small measure, to the fact that asimple cadmium salt and acid give very poorplates. The growth of trees occurs to a remarkable extent from such baths. The sulphate and chloride baths are very poor and the fluoride and fluoborate baths, though somewhat better, have other objectionable features: fumes, expense, etc.

From a study of various acid cadmium plating baths, such as the cadmium sulphate bath containing sulphuric acid, it has been found that such .baths are practically useless because the plate obtained is coarse grained, the throwing power of such baths is poor and treeing is very extensive. It is the object of this invention to produce an acid cadmium bath which in the electroplating operation will give a cadmium plate with good grain refinement, eliminate treeing and have satisfactory throwing power.

The use of acid cadmium baths has been confined almost totally to electrorefining and in the separation of cadmium from other metals in certain analytical procedures. The electrorefiners have employed various natural organic substances as addition agents, for example, gelatin,

and various glucosides, saponin, etc. These'particular complex organic compounds produce compact plate, and reduce the growth of trees to a minimum or eliminate them completely. It is possible to get bright plates from such baths, but the plates are very brittleand usually pitted. These organic agents hydrolyze in acid solution to simpler molecules having no beneficial efiect on the plate. The rather rapid deterioration of such a bath which occurs simply on standing is very objectionable from theelectroplaters standpoint. This invention contemplates an acid cadmium plating bath having as an addition agent an organic compound or compounds of uniform composition and which are sufficiently stable so that in the practical operation of the hath no decomposition is noticeable. I

It is an object of this invention to produce a properly compounded acid cadmium electroplating bath that will give a ductile matte plate with a strong bond to steel or aluminum and that willeliminate treeing in the. electroplating operaon. This object has been achieved by adding to the acid cadmium bath an addition agent from the group of water soluble naphthol compounds. These compounds when used as an addition agent in an acid cadmium bath produce grain refine ment, reduce or eliminate treeing and promote A large number of benzene and naphthalenethe throwing power of the acid cadmium bath.

1-8 dihydroxy naphthalene 3-6 disulphonic acid because of lower solubility. The degree of sulphonation should preferably be'such that too great a solubility is not obtained, excessivesolubility decreasing the interfacial activity of the compound. Thus 2-naphthol-3-fi-disulphonic acid is less effective than any of the naphthol monosulpho'nicacids tested; r

The introduction of a group which decreases solubility improvescompounds which are too soluble for maximum effect. Thus l-naphthyl' amine-8-hydroxy 3-6-disulphonic acid is more effective than 2 naphthol-3-6-disulphonic acid.

The position of the hydroxy and sulphonic groups makes some difierence in effectiveness as 5 shown below, where the naphthalene derivatives have been arranged in order of decreasing efliciency.

' SOaH SOaH f NH:

sour "soul SOaH The amounts'reduired'for maximum efiect are given beneath the formula of the compounds.

The 2-naphthol-6-sulphonic acid was studied in detail. Best results iwere obtained under the following conditions: i

Oz./gal. Cd 3 6 12 40 OzJgal. free Bison.-- .4-2 .4-a.5 .4-13 galgal. addition agent .25.7 .25-.7 .25-.7

e current density range ate is obtained is where visible gassing begin over the surface of the plate The .plate then -tends to become powdery crystalline. Below theglower limit of the current 50 density range for d' e plate blackish velvety he current density range areas tend to form. for-ductile plate the. white. The optimuln- K value for long plating, that is, over one-half 55 hour plating time. (with longer plating burning occurs onedges. Ifihe cathode is moved or the solution agitated, th endency for burning is greatly reduced, ms the agitation makw possible the use of higher-current densities, for ex- .oo ample, in the 12 ozJ/gal. cc bath, the still plate range of 60 ampi/sq. ft. can be raised to -70 amp/sq. ft. byfeven moderate agitation.

The concentration, of acid is not critical except in the low metal baths (6 and 12 ozJgal. 65 Cd) where increasing acid concentration lowers the visible gassing range appreciably. For example, in the 6 oz./gal;'ffCd bath 7 oz./gal. free H2804 lowers the current-density range of ductile" plate to 5-15 amp/sq. ft. It has been found that the adherence of cadmium coatings from cyanide baths, both plain and with such addition agents as described in United States Patent No. 1,692,240 or in United States patent application Serial No. 83,347, is

'75 much improved byth e interposition between it e is always a soft matte-. current density is the best herent cadmium plate upon a metal base which comprises electrodepositing said cadmium from and the basic metal of a thin coating of cadmium applied in the baths described above.

I claim:

1. The method of obtaining ductile matte adherent cadmium plate upon a metal base which 5 comprises electrodepositing said cadmium from an acid cadmium solution in the presence of an addition agent from the group consisting of naphthol sulphonic acids.

2. The method of obtaining ductile matte adherent cadmium plate upon a metal base which comprises electrodepositing said cadmium from an acid cadmium solution in the presence of an addition agent from the group consisting of mono-hydroxy naphthalene mono-sulphonic F acids. 3. The method of obtaining ductile matte adherent cadmium plate upon a. metal base which comprises electrodepositing said cadmium from an acid cadmium solution in the presence of an addition agent consisting of 2-naphthol-6- sulphonic acid.

4. The method of obtaining ductile matte adherent cadmium plate upon a metal base which comprises electrodepositing cadmium from a cadmium sulphate solution containing free sulphuric acid in the presence of an addition agent from the group consisting of naphthol sulphonic acids.

5. The method of obtaining ductile matte adherent cadmium plate upon a metal base which comprises electrodepositing cadmium from a badmium sulphate solution containing free sulphuric acid in the presence of an addition agent from the group consisting of mono-hydroxy naphthol mono-sulphonic acids.

6. The method of obtaining ductile matte adherent cadmium plate upon a metal base which comprises electrodepositing cadmium from a cadmium sulphate solution containingfree sulphuric acid in the presence of an addition agent consisting of 2-naphthol-6-sulphonic acid.

'7. The method of obtaining ductile matte adherent cadmium plate upon a metal .base which comprises electrodepositing said cadmium from a cadmium sulphate solution containing free sulphuric acid in the presence of an addition agent from the group consisting of 2-naphthol-6-sul- 'phonic acid ranging in concentration from .2547 oz./ga1. of solution.

8. The method of obtaining ductile matte ada solution containing from 3-12 ounces cadmium per gallon of solution, from .4-13 ounces free s'ulphuric acid per gallon of solution, and .25-.7 ounce 2-naphthol-6-sulphonic acid per gallon of solution, and a current density ranging from 10 amp/sq. ft. upward to where visible gassing begins over the surface .of the plate.

9. A bath for electrodepositing ductile matte adherent cadmium plate comprising a solution of a cadmium salt containing free acid and an addition agent from the group consisting of naphthol sulphonic acids.

10. A bath for electrodepositing ductile matte adherent cadmium plate comprising a solution oil av cadmium salt containing free acid and an addition agent from the group consisting of mono-hydroxy acids.

naphthalene mono-sulphonic 11. A bath for electrodepositing ductile matte adherent cadmium plate comprising a solution of a cadmium salt containing free acid and an addition agent consisting of 2-naphthal-6-sul phonic acid.

aaaasaa 12. A bath for obtaining ductile matte adherent cadmium plate upon a metal base which comprises electrodepositing said cadmium from a solution of cadmium sulphate and free sulphuric acid and an addition agent from the group consisting of naph-thol sulphonic acids.

13. A bath for obtaining ductile matte cadmium plate upon a metal base which comprises electrodepositing said cadmium from a solution 10 of cadmium sulphate and free sulphuric acid and an addition agent from the group consisting of mono-hydroxy naphthalene mono-sulphonic acids.

14. A bath for obtaining ductile matte cadmium plate upon a metal base which comprises electrodepositing said cadmium from a solution of cadmium sulphate and free sulphuric acid and an addition agent consisting of 2-naphthol-6- sulphonic acid.

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